ERIC WESTERVELT, HOST:
There are more twins in the millennial generation than any other generation, which was pretty obvious if you turned on the TV in the '90s when millennials were growing up.
(SOUNDBITE OF FILM, "IT TAKES TWO")
ASHLEY OLSEN: (As Alyssa Callaway) Wow, there really is two of us. Don't you find this odd?
MARY-KATE OLSEN: (As Amanda Lemmon) No. This is weird. This is really, really weird.
WESTERVELT: That, of course, is Mary-Kate and Ashley Olsen. They're two of the million super-cute extra babies born between 1981 and 2012, all of whom might be hurting the economy. Here's NPR's Rebecca Hersher.
REBECCA HERSHER, BYLINE: Let's get one thing out of the way first. Everyone in this story loves twins - even this guy.
MARK ROSENZWEIG: Well, basically, we would prefer that people were not twins to being twins.
HERSHER: Mark Rosenzweig is an economist. His career is built on studying twins. But, if he's being honest, he thinks twins are bad economic news. First, there's healthcare costs. Twins are more likely to be born prematurely, which can lead to all kinds of expensive medical problems. And then there's birth weight. He did a study based on hundreds of female twins in Minnesota that looked at the effect of birth weight on lifetime earnings.
ROSENZWEIG: The birth weight of twins are, on average, about 28 ounces lower. So the earnings result was 16 percent lower, related to the fact that they had lower birth weight.
HERSHER: Yeah, you heard that right. On average, girl twins make 16 percent less money over their lifetimes, just because they're born less chubby. Unless you think it's only the girls who are a problem. Multiple studies have also found low birth weight correlates with less educational success in boys, which also means earning less money. And then there's the stress on a family of bringing home two babies at once. Here's another person who loves twins.
NANCY SEGAL: As a twin researcher, of course, I want lots of twins in the population.
HERSHER: Nancy Segal runs that Twin Studies Center at Cal State Fullerton.
SEGAL: The birth of twins - it's usually greeted with a great deal of shock. A two-person stroller, two cribs, two of everything, basically.
HERSHER: Double the carpools, double the college payments - raising all those extra millennial twins has been hard on family budgets, plus the cost of having them in the first place.
The main reason for the twin-boom in the '90s was a new, expensive technology called in vitro fertilization which, in its early days, frequently produced twins, triplets and more. But despite the costs, Segal doesn't buy that twins are a bad thing for society. She points out twins tend to support each other emotionally and tend to live closer to each other and to family than regular siblings, which could make them more available to care for aging parents. And being twins might just help them economically, too.
MATT GRADNANI: I'm Matt Gradnani.
MIKE GRADNANI: I'm Mike Gradnani, and we are both 25 years old.
HERSHER: The Gradnanis are identical twins, and they're really, really close. They went to college together, played football and rugby together. They go to bars together, but they're not into the same kinds of women, if you were wondering. And, at 25 years old, they live together in an apartment they own together, which they could afford because there are two of them.
MIKE GRADNANI: I mean, we both kind of felt that it'd be smarter in the long run to put money in our own investment instead of someone else's pocket. And, ultimately, the two of us could afford a lot more space together than we could individually. So...
MATT GRADNANI: It's our hometown.
MIKE GRADNANI: It's our hometown that we grew up in.
HERSHER: And Mike and Matt even co-own a successful business selling real estate. How is that for hurting the economy? They are just two of the 1 million extra millennial twins entering the workforce right now and starting families of their own in the coming years. The ultimate economic impact of all those twins is yet to be known. Rebecca Hersher, NPR News.
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